There are some questions regarding teleconverters - IQ achieved, AF, apperture etc. Having read great Tale of Two Teleconverters
http://www.billmajoros.com/photoalbum/categories/new/Teleconverters/index.html I made a test myself.
Assumptions:
1. Controlled lighting environment
2. Tripod
3. Mirror up
4. Remote shutter
5. Several shots with different appertures, shutter speeds, liveview - best shot chosen
6. No sharpening, contrast etc.=0, DPP from RAW to JPG, Quality=10
Gear used: 7D, EF 70-200 F4 LIS (IS off), EF1.4II, EF2.0II
Below you will find the result in three sections
A. 100% crop of some area possible to make comparisons, constant width=500px
B. Almost the same area, different file sizes
C. Almost same area, JPG downsized to width=500px
Below in this post images from section A:
100% crop of some area possible to make comparisons, constant width=500px